Microcontroller devices capable of relatively high throughput WiFi (IEEE 802.11x) wireless protocol communication have been employed to implement wireless communications on battery operated devices for Internet of Things (IoT) applications. In a typical IoT ecosystem there is seldom a requirement for WiFi communications on such a battery operated device. In many cases, the need for WiFi communications on a battery operated device is associated with response times of the order of seconds, i.e., a button is pressed on the device or a sensor is activated on the device and in a matter of a few seconds something needs to happen, for example, music is to be streamed, video is to be recorded/sent or other kind of data transfer is to occur. Thus, WiFi operation is rarely needed, and then only for a short period of time.
WiFi is a wireless protocol which requires a battery-operated WiFi device to remain actively associated with a wireless WiFi access point (AP) to enable bidirectional WiFi communication. Thus, the battery-operated WiFi device maintains an active WiFi connection while the battery operated device is in use, and dissociates with the AP at other times when the device is not in use in order to reduce power consumption. To reduce power consumption, the wireless association between the device and a wireless access point (AP) is stopped, and all wireless communication-related hardware is shut down on the device. Thus, disassociating with the AP is an action taken by the application layer to stop using WiFi and to shut down the radio. Drawbacks of employing this approach to reduce power in conventional WiFi operation battery operated devices include long response time due to the need for the battery operated device to re-associate with the AP before sending data. This may be of issue where faster response times are desired or needed for particular device operation.
Other drawbacks of temporarily dissociating with the AP include the limitation of single direction access from the battery operated device. This means that the battery operated WiFi device can request a wireless connection to the AP, and then send information to the WiFi network. However, a wireless connection to the device cannot be established in the opposite direction from the AP side while the battery operated device is not associated because all the WiFi wireless communication hardware in the device is shutdown at this time. This single direction access characteristic limits the capabilities of many IoT applications. For example, an event occurring at a battery operated IoT device (such as motion detected by a surveillance camera) is capable of triggering wireless reconnection to the AP so that video information can be sent from the device over the network. But on demand usage of the camera cannot be triggered from the AP side by a user because the AP side cannot request a connection to the device while its WiFi communication hardware is shutdown.
WiFi wireless communication protocol includes a beacon based Low power mode option that utilizes delivery traffic identification (DTIM) and traffic identification map (TIM). This WiFi Low power mode allows the device hardware to stay connected with the AP by only monitoring the wireless communication medium at pre-determined beacon times, mainly at the DTIMs that cover broadcast and multicast messages. This allows the device to have informationremain associated, and also to send and receive data to the AP. The beacons are spaced by hundreds of milliseconds (300 ms in the lowest commonly used duty cycle case). However, this results in a level of activity that is at least one order of magnitude higher than that required by an application that has a response time in the order of seconds. Thus, using WiFi wireless protocol for a surveillance camera, doorbell camera or other similar battery operated device either results in limited single direction access (while there is no association with the AP) or relatively large power consumption and battery drain.